Nanofluids are found to have good optical and thermal properties as direct sunlight absorbers in solar collectors. In this article, Co-H2O nanofluids were prepared through two-step method. The photothermal properties of nanofluids were investigated under different magnetic field intensity. The effect of Co-H2O nanofluids on the efficiency of a direct absorption solar collector was also investigated experimentally. The experimental results show that the applied magnetic field can enhance the solar absorption ability of Co-H2O nanofluids, and has an optimal magnetic field intensity 30Gs. The highest temperature of Co-H2O nanofluid (0.04wt%, 30Gs) is increased up to 39.5% compared with deionized water. The maximum efficiency of direct absorption solar collector with Co-H2O nanofluid under 30Gs magnetic field (0.1wt%, 30nm) is increased up to 51.70% and 13.24% compared with water and Co-H2O nanofluid without magnetic field, respectively. The results indicate that the magnetic field has the potential to effectively improve the solar absorption capabilities of direct absorption solar collectors with magnetic nanofluids.

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